The present invention relates to radial truck tires, preferably radial medium truck (RMT) pneumatic tires.
The treads of RMT tires are subject to puncture from stones and other sharp objects in the road surface. In many cases, although the puncture is not deep enough to penetrate the belt package and destroy the tire, it is deep enough to expose the steel reinforcement cords of the belt package to water and air, and such exposure can cause the belt package to corrode. This problem is aggravated when tires are used in mixed service, i.e., partially on paved surfaces and partially on non-paved surfaces, such as exist on the Alaska Highway. Although rust does not significantly affect the strength of the reinforcement ply, many tires are scrapped if excessive corrosion is observed on the top belt when the tread is skived from the tire in preparation for retreading.
In the conception of the present invention, it was proposed to replace some of the steel reinforced belts in the belt package, and at least the top belt, with a non-corrosive belt made with organic reinforcement, or to add such a belt to the top of the belt package. It was decided to test large diameter, obround nylon 66 monofilaments for such purpose. Monofilaments of similar structure have been used in radial ply tires as described in U.S. Pat. No. 4,850,412 issued to Gupta, Jul. 25, 1989.
A pneumatic radial medium truck tire of the invention comprises at least one pair of parallel annular beads, at least one carcass ply wrapped around said beads, two to twelve belts or breakers disposed over the carcass ply in a crown area of the tire, tread disposed over the belts or breakers, and sidewalls disposed between the tread and the beads. The majority of the belts or breakers in the tire are reinforced with steel filaments or cords, and the remaining belts or breakers are reinforced with organic polymer filaments or cords. The top belt or breaker is reinforced with organic polymer filaments or cords.
In an illustrated embodiment, the organic filaments or cords are nylon monofilaments which have an obround (oblong) cross section and are at least 2000 denier (2200 dTex) and have a tenacity of at least 3.5 g/denier (31 cN/Tex), an initial modulus of at least 30 g/denier (265 cN/Tex), an elongation at break of at least 17% and a shrinkage of at most 6%.
In various embodiments of the invention, the top belt or breaker ply is a nylon monofilament reinforced ply wherein the reinforcement cords have an angle of 0xc2x0 to 35xc2x0 with respect to the tire. In some such constructions,an organic monofilament reinforced ply is used as an overlay/top breaker wherein the ply extends beyond the edges of the other breakers, and the angle of the reinforcing cords are maintained at the same angle as the steel reinforcement cords in the breaker ply next radially below, or are at angles which cross said steel reinforcement cords.
Specific constructions of such tires are also claimed.
It is an object of this invention to reduce corrosion of RMT tires caused by penetration of the tread by sharp object of this therefore improve their retreadability. Other objects of this invention will be apparent from the following description and claims.